The present invention relates to torque sensors and more particularly to a small diameter torque sensor having injection molded magnets disposed on a substrate rotor.
In a conventional torque sensor, a torque is sensed as it causes a rotational deformation in a shaft, upon which the torque acts. As the shaft deforms, a difference develops between the angular positions of the shaft at locations along the shaft. A non-contacting small diameter torque sensor provides a flux density output that depends upon the change in angular position between a first shaft position and a second shaft position. When it is desired to measure a torque applied to a shaft, such as a control shaft of an electric steering system of a vehicle, an upper segment of the steering control shaft and a lower segment of the steering control shaft may be coupled by a torsion bar torque sensor such that a torque applied to the steering wheel may be determined and provided to a controller to aid in controlling torque assistance to be supplied to the steering system.
In such systems, it is generally desirable to have a non-contacting torque sensor that provides relatively high magnetic field (Gauss/deg) and rotational accuracy (low harmonic/rev). Unfortunately, previous attempts to satisfy these requirements have succeeded in improving magnetic field response but have also entailed significant cost, manufacturing complexity, and signal noise (i.e., ripple). One reason for these drawbacks of conventional small diameter torque sensors is their reliance on traditional radially-oriented, sintered, neodymium magnets to create the magnetic field that is used as the input to the sensor. The cost of sintered neodymium magnets is very high and this in turn increase the manufacturing cost of the torque sensor.
Accordingly, it is desirable to have a non-contacting torque sensor that provides relatively high magnetic field and rotational accuracy without the cost associated with sintered neodymium magnets.